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Full text of "The manufacture and properties of iron and steel"

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INTRODUCTION.
9.
tne amount added is very small and the carbon thus carried into the bath is trifling.
The resulting steel is poured into a ladle, and the slag., being very light, floats on the top. The steel is then tapped from the bottom, the separation of metal and slag being perfect. Minute cavities of slag are often found in steel, but these come from internal chemical reactions, or sometimes from dirt in the mold. They do not arise from mixture of the metal and slag when poured in the way that is almost universally used in Bessemer and open-hearth works.
In this acid process there can be no removal of phosphorus or sulphur, and as no steel is allowed to contain over one-tenth of "one per cent, of either, it is plain that the pig-iron must not contain more than this allowable amount. It has been shown, in the discussion of the manufacture of pig-iron, that the phosphorus in the ore will appear in the nietal. Consequently if the ores of any district contain more than one-twentieth of one per cent, of phosphorus, which will give one-tenth of one per cent, in the iron, that district cannot possibly use the acid Bessemer process., If they do contain as little as this, then this process is the cheapest method of making steel that has ever been discovered or probably ever will be.
THE BASIC BESSEMEE PEOCESS.
The basic Bessemer process is similar to the acid Bessemer, both being founded upon the general truth that if cold air be blown through pig-iron, the combustion of the impurities in the iron will furnish sufficient heat to keep the metal in a fluid state. In the acid process it has been shown that only two elements are thus burned, viz., silicon and carbon, and that the silicon supplies most of the heat.
In the basic process the lining is made of basic material, usually of hard burned dolomite, which is a limestone containing from 30 to 40 per cent, of magnesia. When the linings are basic, it is a bad thing to have much silicon in the iron, because when silicon is oxidized it forms silica (Si02), and this attacks the lime lining. The percentage of silicon is therefore kept as low as possible, and this makes it necessary that some other source of heat be provided. This is the more necessary because more heat is needed in the basic process than in the acid, on account of the lime which is added in the converter and which must be melted during the operation.
The element used to take the place of silicon and supply heat is